Coded track circuit railway traffic controlling apparatus and switch control



J. J. VAN HORN 2,430, 1 CODED TRACK CIRCUIT RAILWAY TRAFFIC CONTROLLING APPARATUS AND SWITCH CONTRQL Filed Sept. 15 1941 4 Sheets-Sheet 1 m 0 R Y m m NW R E o 0 WSNQ 5% a? fiwmm mma fi w 5 QLZ Nov. 4, 1947.

CODED TRACK CIRCU IT RAILWAY TRAFFIC CONTROLLING APPARATUS AND SWITCH CONTROL Filed Sept. 13,' 194 1 4 Sheets-Sheet Nov. 4,1947. J J. VAN HORN 2,430,314

R i i am 1P1 I 45157114410012 15 0 In- 8M 85m am my,

Y mvsu-roa J2me; Ibnfz'omz BY HIS ATI'ORNEY' 1947- J. J. VAN HORN CODBD TRACK CIRCUIT RAILWAY TRAFFIC CONTROLLING APPARATUS AND SWITCH CONTROL I 4 Sheets-Sheet 3 Filed Sept. 13 1941 5 NmQ UH ENQ fiw LT r INVENTOR J1me [612110011 ,BY

H75 A'IITORNEY VAN HORN 4 Sheets-Sheet 4 Nov. 4, 1947. J J,

CODED TRACK CIRCUIT RAILWAY TRAFFIC CONTROLLING APPARATUS AND SWITCH CONTROL Filed Sept. 13, 1941 baggy INVENTOR James Vin Homz H15 ATTORNEY Patented Nov. 4, 1947 CODED TRACK CIRCUIT RAILWAY TRAFFIC CONTROLLING APPARATUS AND SWITCH CONTROL James J. Van Horn, Pittsburgh, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application September 13, 1941, Serial No. 410,717

8 Claims. 1

My invention relates to railway trafiic controlling apparatus and is more particularly directed to the control of trafiic in a single track, twodirection system wherein centralized traffic control or other suitable manual control is used for establishing the traffic direction A distinguishing feature of my system is that it is of the normally deenergized track circuit type and dis-v penses with all control line wires except for the C. T. C. coded line circuit, if C. T. C. is used. The present invention is an improvement on the invention disclosed in my copending application for Letters Patent of the United States Serial No. 410,504, filed on September 12, 1941, for Railway traffic controlling apparatus, now Patent No. 2,344,573, dated March 21, 1944.

One object of my invention is to provide a normally deenergized track circuit system of signaling for traffic moving in either direction on a single track, employing no control line wires for the usual signaling functions. Another object of my invention is to provide means for retaining the established trafiic direction as long as a train is approaching or occupying the single track stretch, solely by means of the track circuit apparatus, without dependence on any circuits or apparatus at the point of control from which the C. T. C. code emanates. A further object of my invention is to provide complete automatic control of electric switch locks A still further object of my invention is to provide a code system of this general character which has a flexibility, safety, and reliability comparable to coded A. P. B. systems employing control line wires. Other objects, purposes and characteristic features of my invention will be apparent from the description which follows:

I accomplish the foregoing objects as follows. I

transmit a suitable C. T. C. code to the field station at the exit end of the single track stretch which results in the application of a normal or master track circuit code of normal relative polarity at that end for setting up traflic in the desired direction over the stretch. This track circuit code is cascaded over the track circuits of the single track stretch to the entrance end where it initiates the supply of a reverse or feed back code of reverse relative polarity during off intervals of the master code. The feed back code is cascaded back to the exit end and when there received, as will be the case when the stretch is unoccupied, permits the reversal of the trafilc direction, but when not received at the exit end, as will be the case during occupancy, the absence of feed back code is used to prevent cutting off the master coded track circuit energy, thus making it possible to retain the new traffic direction as long as a train is approaching or occupying the single track stretch. I make use of polarity of the master and feed back track circuit codes for performing the selective functions which prevent conflicting moves and which provide safe operation. I also employ these .codes for the control of electric switch locks whereby, in order to permit a train to leave a siding switch, it is merely necessary for the operator to set up traflic in the proper direction, as required by the train on the siding. If a train occupying a siding desires to follow a train on the main track, no action on the part of the operator is required.

I shall describe two forms of apparatus embodying my invention and shall then point out the novel features thereof in claims.

Figs. 1A to lDinclusive, of the accompanying drawings when placed end to end with Fig. lift at the left, are a diagrammatic view showing a single track, two-direction signaling system embodying my invention. Fig. 2 is a diagrammatic view showing a portion of the apparatus of Fig. 1 applied to manual electric switch lock control, also embodying my invention.

Similar reference characters refer to similar parts in each of the several views.

In this system, I employ but two codes, these being the usual '75 and per minute codes which are adequate for providing a three indication system. These codes are merely illustrative since other code rates and either more or fewer codes may be used as demanded by practical operating requirements of the particular system.

Referring to the drawings, I have shown a stretch of single track between two passing sidings PSI and PS2, this stretch being divided into track circuit sections by means of the usual insulated rail joints at locationsD, E, F, G, 1-1, I, J, and K. Locations D, F, I, and K are signal locations; E and G are ordinary cut-section locations; and H and J are cut section locations necessitated by the presence of turnouts and electric track switches in that vicinity. Two track switch locations are shown, one of these G--II being at a cut section, the other I-J being at a signal location.

At each end of the stretch is a field station unit connected by the usual C. T. 0. line with a control ofiice (Fig. 1A) from which are transmitted control codes for selectively operating a traffic direction control relay at each of the field stations. The field stations, in turn, transmit certain indication codes to the control oflice when conditions are proper, thereby informing the operator of the indications provided by the headblock signals and of the traffic conditions within the stretch. This C. T. C. apparatus, of itself, forms no part of my present invention and it is unnecessary to show this apparatus in detail, for an understanding of my invention. Reference may be had to Letters Patent of the United States No. 2,229,249, granted to L. V. Lewis on January 21, 1941, for a detailed description of a C. T. C. system such as can be used herein, and I have used the same reference numbers as are used in that patent to designate certain terminal wires of the field station unit which perform analogous functions.

The traffic lever B at the ofiice controls traffic movement over the single track stretch. When in its right-hand or R position, this lever permits eastbound moves and when in its lefthand or L position, it permits westbound moves. The center position of the lever may be used to cause the track circuits to become deenergized. This lever will ordinarily be a part of the C. T. C. machine and when moved, initiates the transmission of a suitable control code over the C. T. 0. line wires which extend throughout the territory controlled by the C. T. C. machine. As mentioned hereinbefore, this code causes selective response of certain traffic direction relays which condition the single track stretch for movement of traffic in the desired direction. The specific control for the trafi'ic direction relays, whether manual, automatic or otherwise, is unimportant and may take numerous suitable forms, as required by the particular installation.

The basic operation of my system depends on the transmission of a master track circuit code over the track circuit and the transmission of a feed back code in the reverse direction over the track circuit during off intervals between impulses of the master code, if the track circuit is then unoccupied. This general type of operation is well known and is disclosed in Reissue Letters Patent of the United States No. 21,783, granted to Herman G. Blosser on'April 29, 1941. In order to obtain proper selective response of the apparatus to each of these two codes, I employ current impulse of positive relative polarity for the master track circuit code, impulses of negative relative polarity being used for the feed back code.

With the apparatus in the condition in which it is illustrated, the last move having been eastbound, Ishall assume that the operator wishes to reverse the traffic direction so as to permit a westbound train to enter the single track stretch. Since the last move is assumed to have been eastbound, the eastbound polarized track relays such as SETRA (having last responded to master code of positive relative polarity) have their contacts occupying the normal position, whereas the westbound polarized track relays such' as SWTRA were last energized on feed back code of negative relative polarity so that the latter relays have their contacts in the reverse position. To reverse the trafiic direction, the operator will move lever 8 to its left-hand or L position so as to transmit a suitable code to cause energization of terminal 81 of the field station unit (Fig. 1A) and so to energize relay 8LFSR, assuming that relays 8RFR and BRSR' are both deenergized so that their back contacts 14 and 15 are both closed. These last two relays check that the stretch is normal and is unoccupied by an eastbound train, as will be described hereinafter. Once relay 4 8LFSR picks up, it closes a stick circuit for itself over its front contact 12 and the back contact H of relay WFB so that the traffic direction cannot be changed until relay WFB is subsequently picked up.

The pick-up of relay GLFSR applies current of normal polarity coded at the '75 or code rate according as the home relay GLAH for signal 6L i deenergized, or energized, respectively, to the track section BRT. This current comprises the master code and is applied to the track in the following manner. The pick-up of relay 8LFSR picks up relay 8LFSM over front contact 92 so that a coding circuit is established for the code repeating relay BRTCTM which may be traced from wire 15B, back point of contact H of relay BLAH, front contact 12 of relay BLFSM, front point of contact l3 of relay 8LFSR, relay SRTCTM, and front point of contact [4 of relay BLFSR, to terminal C. The coding action of relay GRTCTM, when relay BLFSR is up, applies master track circuit code of positive relative polarity from the track battery TB over an obvious circuit which includes the coding contact [5 of relay BRTCTM, front points of contacts is and ll of relay SLFSR, back contact l8 of relay BRSR, and front contacts l9 and 20 of relays BRKM and BTR, respectively. Relay BRSR is the stick relay for following moves, and relay BRKM is the usual approach locking relay, ETR being the track relay for section 5T.

This 75 code of positive polarity will be received at the cut section location E and will energize the polarized relay GWTRA over an obvious circuit which includes the back point of contact 2| of relay BWCTM. The polar contacts of relay BWTRA will accordingly be reversed from the position shown and will become closed in the normal position so that the biased polar relay GWTR will begin to respond to the master track circuit code. This response of relay BWTR will occur only if the position of the polar contacts of relay BWTRA corresponds with the polarity of the track circuit code being received as otherwise the armature of relay BWTR would be held against the backstop in its deenergized position due to the biased polar characteristic of this relay. Relay GEFB will remain deenergized because its circuit is interrupted at polar contact 22 of relay SWTRA.

The code operation of contact 23 of relay GWTR will cause code response of the code repeater relay EEICTM by virtue of a circuit which includes the coding contact 23, normal contact 24 of relay BWTRA, and back contacts 25 and 26 of relay EEFB. Accordingly, master track circuit code of positive polarity will be repeated from section BRT around the cut section location E and into section BART. The code supply circuit extends from battery TB, and includes the front point of contact 3| of coding relay BECTM and the back points of contacts 32 and 33 of relay GEFB. This master code of positive polarity will be detected by relays 8WTRA and BWTR at location Fin the same manner as at location E and will be decoded in well-known manner by the decoding apparatus which includes the decoding transformer 813T, the '75 and 180 code detecting relay BWI-IR and the 180 code detecting relay BWDR. Relay SWTFSA is a slow acting repeater of the front contact 35 of relay BWTR and controls the application of current to the decoding transformer EDT over its front contact 37. If the code is 75 (as assumed), only relay 8WHR will be energized so that signal 3W will display a caution indication,

but if the code is 180, both relays BWHR and BWDR, will be energized so that signal 8W will display a clear aspect.

The track circuit fil tT will be supplied with 130 master code of positive polarity because relay will be deenergized and relay EWHR will be energised. thus causing operation of relay EE'CTM on 18% code. The coding circuit for relay SECTM extends from the 180 code wire E8013, over the front point of contact 2'! of relay BWHR and the back points of contacts 28 and 29 of relay llEF'B, to the common source terminal C. The master track circuit code will be applied from battery TB over the front point of contact 39 of relay @EICTM, back contacts B l and 35 of relay SEFB, and the winding ,of the approach relay EWAR. The approach relay need be used only if it is desired to approach light the intermediate signal 3W as a, means of conserving the energy of the signal lighting source. Receipt of 180 code of positive polarity at location G will energize the polarized relay SAWTRA in a direction such that its polar contacts will reverse from the po 1 shown, whereby relay SAWTR will also w lllil code, as previously explained in connection with locations E and F.

ection G--H is a short detector section e turnout at location H. No code is supthe track circuit AT of this section, but he control of the electric switch lock AW is in a novel manner by the apparatus For the present, it will be .ing the code from section BRT into the section SARI, around the detector section.

Relay EBAECTM will accordingly follow 180 code supplied over coding contact 38 of relay BAWTR,

polar c tact 38 of relay SAWTRA, front contact of y ATWM, and back points of contacts ii of relay BAEFB. Relay QW'TR at location I will respond to the code delivered by relay SAECTM, as before, and in so doing will repeat the code into section lfiLT by virtue of the code operation of relay QECTM. The circuit for this relay is similar to that traced for relay GAEJCTM and includes coding contact 43 of relay EWTR, polar contact (i i of relay QWTRA, front contact lli of relay BTWM, and back points of contacts 36 and d1 of relay QEFZB. The short detector ection ET is similar to the section AT and is necessitated by the presence of the track switch for the turnout at location J.

The 180 master code of normal relative polarity supplied to section lilLT over the front point of contact d8 of coding relay QECTM will operate relay lllLTR at the 180 code rate and so will cause an impulse output to be delivered from the decoding transformer ltDT for operating the slow acting relay SLER. Ihe circuit for this relay extends over the rectifying contact 59 of relay lllLTR and polar contact 56 of relay IGL'IRA. The pick-up of relay iiLFl-t will cause terminal 89 of the field station unit to become energized so that an indication code showing unoccupancy of the stretch will be transmitted to the control office. The coding action of decoding transformer ltDT will supply an impulse code from the transformer lilDT over the back contact M of relay ERFSM' and the back points of contacts 53 and 52 of relay SRFSR, for operating the relay IQLTCTM. Operation of this relay will cause a feed back code of negative relative polarity to be supplied'from battery TB to the track circuit IULT during the oil intervals in the master track circuit code. .The circuit for supplying this reverse or feed back code includes the front point of contact 54 of relay lllLTCTM, back points of contacts 55 and 56 of relay BRFSR, back contact 5'! of relay lElLSR, and front contacts 58 and 59 of relays EGLKM and l ITR, respectively. Thus feed back code will not be applied unless track circuit l lT is unoccupied and the entrance signal lElL is at stop. The stick relay IBLSR for signal IGL (indicated by back contact 51) performs the same function as relay BRSR at location D and is controlled in an identical manner with that shown for the latter relay, over contacts of the corresponding relays associated with signal lElL. Accordingly, the control for relay lilLSR. will be clear without a repeated showing in the drawing. Similarly, the approach loclnng stick relay SBLKM and track relay l ETR have been indicated merely by their contacts 53 and 55 which correspond with contacts iii and 26 of relays BRm and 5TB. The purpose served by these contacts in checking the stop position of the headblock signal ML and the unoccupancy of the approach section is so clear and well known that it is deemed unnecessary to complicate the disclosure by showing additional control circuits.

Continuing the description of feed back code transmission, at location J, the negative polarity feed back code will be received by relay SETRA which will now reverse its contacts from the position shown in the drawing, thus making it possible for the biased polar relay QETR to follow the impulses of the negative polarity code. Relay QWFB will now become energized over polar contact Ell of relay EETRA in its reverse or righthand position, and relay QEHR will continue deenergized. The pick-up of relay QWFB closes an impulse circuit for relay SWCTM over the front points of contacts 6! and 62 and prepares a negative polarity feed-back code track feed circuit over its front contacts 83 and 64 which circuit supplies the feed. back code to section BART over the front point of contact 65 of relay SWCTM. At location H, the negative polarity feed back code will reverse the polarized relay BAETRA, so that relay SAWF'B will be picked up on the impulse output, over polar contact 66 of relay 8AETRA in its reverse position, front contact 61 of relay ATWM, and rectifying contact 68 of relay tAETR. In an analogous manner, the pickup of relay GAWFB will cause impulse operation of relay BAWCTM at location G and the supply of negative polarity feed back code to section SRT over the front point of coding contact 69 of this relay.

Similarly, the negative polarity feed back code will be repeated into section EART through the pick-up of relay BWFB, and into section BRT through the pick-up of relay EWFB. At location D, this negative feed back code will reverse relay SRTRA and cause pick-up of the westbound block indicator relay WFB over polar contact Ill in its left-hand position. The pick-up of relay WFB will open the stick circuit for the westbound traffic direction relay 8LFSR at back contact 11, but this relay will not release because its other stick circuit which includes its own front contact 12, a circuit between terminals 88 and 81 of the field station unit (closed under the assumed condition), and back contacts M and 15 of relays BRFR and BRSR will be closed. However, a code can now be transmitted from the control office to,

release relay QLFSP). The pick-up of relay WF'B causes the transmission of an indication code which lights the west-bound block indicator lamp WBK which indicates that the stretch in unoccupied and that the westbound headblock signal [BL is at stop, since feed back code has now been cascaded from the entrance to the exit end. Since relay GLFR. at location K is energized a control code may now be transmitted to the field station for clearing the headblock signal IUL so as to permit traiiic to enter the'stretch.

The clearing of signal [L releases the approach locking stick relay I BLKM in the usual and well-known manner so that front contact 58 will open and will interrupt the supply of feed back code to the stretch. In consequence, relay WFB at location D will release, closing the stick circuit for relay SLFSR at its back contact 1| (front contact 12 of SLFSR now being closed) to maintain the established traffic direction, since relay SLFSR cannot now be released by the operator without first restoring signal IOL to stopprovided the stretch is still unoccupied. Accordingly, the absence of feed back code prevents cutting off the master code at location D, thus retaining the established traific direction. Once the stretch is occupied, there is no possibility of the feed back code getting through to energize relay WF'B atlocation D, so that the absence of feed back code provides trafiic locking against areversal oftraific by the operator, solely by means of track circuit apparatus and independ-' ently ofany apparatus at the control office. Once the train clears the stretch, feed back code will get through, as will be describedhereinafter, so that reIay WFB will pickup, permitting a change in thetraihc direction.

When relay 8LFSR is energized to apply-master code tothe single track stretch and the feed back code is being received to energize relay WFB at location D, there is a possibility that when relay BLF'SR is later deenergized following the completion of a traflic movement, the feed back code may operate relay GRTCTM over the back points of contacts I3- and [4' of relay BLFSR. Such undesired operation would ordinarily continue untilinterrupted manually. To prevent this condition, I employ a slow release repeater relay BLFSM' ofreIayBLFSR, interposing a back contact T6 of this relay into the feed back circuit for relay SRTCTML Relay 8LF'SM should be sufficiently slow in releasing to permit the coding actionto stop before the back contacts of this tercode is shunted out and the code responsive apparatus at location K will cease'operating. The feedback circuit will continue to remain open at back contact-'! of relay lllLSR which became energized when the train entered track section l l-T'wi'th the hom'e'relay for signal [OLA or IBLB- energized. The control or relay IULSR is not shown as it is analogous to the control ofrelay GRSR atlocation D; The master code will, now ever; remain efiective insection 8ART and in" the remaining sections. Nothing significant will happen when the train enters the detector section BT except that the track relay BTR will release. When the train passes the intermediate signal 9W and enters section 8ART, however, the master code will be shunted so that the code respon'sive apparatus responding to the master code will be deenergized. Clearing of section I!) LT and the detector section ET by the train will re-introduce master code of the '75 code rate into section IOLT in the usual manner for a following westbound train. The apparatus for applying code to permit a following move is well known and is not shown in detail at location I. It is shown more complete at location F, however, and it will be obvious that when the train passes out of section 8RT, having picked up the directional stick relay BWSR in the usual manner, '75 code will be applied to section 8RT because of the 75 code energization of relay 8ECTM over the front contact 93 of relay" 8WSR, back point of contact 21 of relay BWHR, and back points of contacts 28 and. 29 of relay 8EFB.

The receipt of '75 code at location K will cause the deenergization of relay HILSR in the usual manner so that feed back code will be applied to track section HJLT as hereinbefore described.

Nothing significant will happen as the train passes over the sections BART and GET (except that the master code will be shunted) until the train vacates the stretch completely. The Westbound trail-lo direction relay 8LFSR will remain energized during occupancy, over its stick circuit which includes contacts ll and ?2 of relays WFB and BLFSR, as pointed out before, so that the traffic direction will be retained until the train passes completely out of sections BRT and ET. Thereupon, the apparatus may be restored by the operator to its normally deenergized condition in which it is illustrated. This can be done by coding the signal IOL to stop, if clear, so that feed back code will be cascaded from location K to location D for energizing relay WFB at the latter location. Thereupon, the operator may send out a code for releasing the traffic relay SLFSR. Release of this relay will discontinue the supply of master code at location D so that all of the coded track circuits of the stretch will become deenergized.

This system is arranged so that operation of the coded track circuit apparatus may be discontinued when their operation is not required. However, it is not essential that operation of the coded track circuit equipment be discontinued and if desired, after a train has passed through the stretch in either direction, the coded track circuit apparatus may be permitted to continue tooperate with the enterin head block signal held at stop so that master code energy is transmittedin one direction over the stretch and feed back energy is transmitted in the opposite direction over the stretch. While the deenergized condition is referred to as the normal condition it is obvious that the condition in which the coded track circuit apparatus is operating and the head block signal is at stop may also be considered to be the normal condition, and during such times coded energy'is normally supplied in both directions over the rails of the track stretch.

Should the operator now desire to establish traffic in'- the eastbound direction, he will move lever 8 to the R position so as to transmit a code to the field station at location K to pick up the eastbound traihc direction relay 8RFSR and thereby initiate a cycle of operation which results in establishing the eastbound trafiic direction over the stretch in a manner identical with that already described for westbound traflic. It will be clear, however, that relay SRFSR may not be energized in an attempt to establish the eastbound trafiic directione'ven though the lever is moved to the R position, if either or both relays 8LFR or lilLSR are energized as will be the case when the westbound traffic direction-is effective in the stretch. Energization of relay 8LFR indicates that master code is being received at the westbound entrance end, whereas energization of relay IDLSR (which corresponds with relay ERSR at the other end) indicates that the Westbound train has accepted the entrance signal.

Referring now more particularly to the control of the electric switch locks for the manually operated track switches WI and W2 at locations H and J, these switch locks are so controlled as to permit a train to enter the main track from the siding provided that the stretch is then unoccupied, or if occupied, the train is moving away from the switch and is beyond the next signal location. In order to permit a train from the siding to enter the main track when the stretch is already occupied, I provide a short track circru't AT and BT ahead of each switch lock for the release of the lock when the main track is occupied. When a train on the siding at location H, for example, is to enter the main track, an unlock of the electric switch lock AW may be secured provided that the stretch is either unoccupied or that a train is occupying a portion of the stretch between the switch WI and the exit end such that master code can be supplied to the track section between the train and the switch location. Assuming westbound traffic, if the stretch i unoccupied, then master code will be efiective in section 8RT for operating relay BAWHR. Also, feed back code will be effective in section BART for operating relay 8AWFB. The same will also be true if a westbound train on the main track has completely vacated section SET because 75 master code will then be efiective in this section so that if the operator codes signal lliL to stop, feed back code will be effective in section 8ART. Accordingly, relays SAWHR and BAWFB will again both be energized. Since relays 8AWFB and EAWHR are both picked up, as previously explained, an operating circuit for electric switch lock AW will be completed over the front contacts it and "a? of these relays, and wires 18, i9, 86 and 85. A similar circuit for energizing the switch lock AW can be traced over front contacts $4 and 95 of relays 8AEFB and BAEHR when traiiic conditions are eastbound instead of westbound. Relay ATWM repeats the deenergized position of the switch lock (contact 83), the energized position of the track relay ATR for the short releasing track section AT (contact 84), and the manual time element release TER (contact 35-). The operation of this apparatus which associated with the electric switch lock AW as well as the operation of the switch lock BW at the signal location and its associated apparatus will be clear without further description.

The apparatus described above provides complete automatic control of the electric switch locks whereby all that is necessary to permit train to leave a siding switch is to have the oper ator set up traflic in the direction in which it is desired to have the train proceed. In case the operator desires to'have the siding train follow a train on the main track, then no action on the part of the operator is required to accomplish this result because an unlock will be automatically obtained. It will be apparent that the above means of control is not limited to the control of an electric switch look, but is broadly useful for controlling any traffic governing device at a location intermediate the two ends of the stretch. Accordingly, although the short detector section AT is desirable in the case of control of a track switch, this detector section may be dispensed with and the sections 8RT and 8AIRT made to adjoin, in other applications of this means of control.

In Fig, 2, I have shown an alternative type of control for the switch lock AW at location E. This control is quite similar to that already described but includes a code controlled relay CCR under the control of the operator at the C. T. C. control office. By transmitting a suitable code, the operator can pick up relay CCR to close the front contact 86 whereby, if both the normal polarity master code and reverse polarity feed back code (as reflected by the energization of the westbound relay pair BAWHR and 8AWFB or the eastbound relay pair SAEI-IR and BAEFB) are received at the switch lock location, the energizing circuit for the lock AW will be completed so as to permit an unlock of the switch.

From the foregoing it will be apparent that I have provided a safe, efiicient and flexible normally deenergized system of signaling for a stretch of single track, two-direction railway, without requiring any control line wires except for the C. T. C. line circuit. By cascading the master code from the exit end to the entrance end and by cascading a feed back code in the reverse direction, I check unoccupancy of the stretch, establish trafiic in a given direction, and permit the entrance signal to be cleared for passage of traffic in that direction. I am also able to retain the established trafiic direction by means of the track circuits themselves without requiring inter-controls on the C. T. C. machine since clearing of the entrance signal or occupancy 5d manner.

Although I have herein shown and described only two forms of apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In combination with a stretch of track over which traffic may move in either direction, an eastbound and a westbound trafiic direction control relay, means for selectively energizing said eastbound or said westbound direction control relay, means effective when said eastbound direction control relay is energized for transmitting rail current impulses of a master code from the eastbound exit end to the eastbound entrance end of the stretch, a code detecting relay adjacent said entrance end responsive to said master code and effective when energized for establishing eastbound traffic, an eastbound directional stick relay adjacent said entrance end which becomes energized when aneastbound train enters said stretch, and means controlled by said code detecting relay and said directional stick relay when either relay is energized for preventing energization of said westbound traffic direction control relay to thereby prevent a reversal of said established trafiic direction.

2. In combination, a section of railway track through which trafiic may move in either direction between the first and the second end of the section, means efiective when master code energy is received at the first end of the section to permit a first signal to be Cleared to authorize traific to enter said section at the first end thereof, means effective when master code energy is received at the first end of said section provided said first signal is at stop to supply impulses of feed-back energy to the section rails at the first end thereof, means eifective when master code energy is received at the second end of the section to permit a second signal to be cleared to authorize traffic to enter said section at the secend end thereof, means efiective when master code energy is received at the second end of said section provided said second signal is at stop to supply implllses of feed-back energy to the section rails at the second end thereof, a first and a second directional relay each having contacts which normally occupy a first position, means operative when train enters said section at the first end thereof for moving the contacts of said first directional relay to their second position and for maintaining them in their second position as long as said section is occupied, means operative when a train enters said section at the second end ereof for moving the contacts of said second directional relay to their second position and for maintaining them in their second position as long as said section is occupied, manually controlled means for supplying master code energy to the section rails at the first end thereof provided master code energy is not beingreceived at the first end thereof and the contacts of said first directional relay are in their first position, means effective only when feed-back energy is being received over the section rails at the first end thereof for discontinuing the supply of master code energy to the section rails at the first end thereof, manually controlled means for supplying master code energy to the section rails at the second end thereof provided master code energy is not being received over the section rails at the second end thereof and the contacts of said secend directional relay are in their first position, and means effective only when feed-back energy is being received over the section rails at the second endthereof for discontinuing the supply of master code energy to the section rails at the second end thereof.

3. In a coded track circuit signaling system for governing train movement over a stretch of track including an outlying switch, a switch lock for said switch, code responsive means responsive to the transmission of. code pulses in both directionstoward said switch for governing the release of said switch lock, means normally acting while the stretch is not occupied by a train for transmitting such code pulses in both directions toward said switch, and means responsive to the presence of a train adjacent the switch for inde pendently governing the release of said switch lock, whereby the switch is locked. by the ap- 12 proach of a train in either direction but may be released for a train to enter the switch when that train is adjacent the switch.

4. In a coded track circuit signaling system for a stretch of single track between the ends of passing sidings divided into a number of track sections, coding means for the respective track sections manually controlled from a distant control ofiice for at times transmitting signal clearing code pulses in one direction over the track rails of the respective track sections and inverse code pulses in the opposite direction over the track rails of a plurality of said track sections in accordance with the direction of traific manually established, means responsive to the presence of a train in one of said plurality of track sections for stopping transmission of said inverse code pulses in the adjoining track section ahead of such train, occupancy indicating means in said con. trol ofiice, and code responsive means for each end of said stretch energized by the inverse code pulses received at that end for governing said indicating means.

5. In a coded track circuit signaling system for single track railroads, a stretch of single track divided into track sections and having an outlying switch associated with one of said track sections, insulated joints in said one track section adjacent the facing point side of said switch, a code following track relay connected across the track rails of said track section on each side of said insulated joints, means normally acting while the stretch is not occupied for transmitting code pulses in both directions over the track rails of said track section, a switch lock for said switch, means efiective only if both of said track relays are energized by code pulses transmitted in each direction toward said switch for governing the release of said switch lock, and release means responsive to the presence of a train adjacent said switch for independently governing the release of said switch lock.

6. In a coded track circuit signaling system for a stretch of track divided into track sections and having signals at intervals governing train movement in opposite directions into and through said stretch, an outlying switch associated with one of said track sections, insulated joints in said one track section adjacent the facing point side of said switch, a switch lock for said switch, means normally acting while the stretch is not occupied for transmitting code pulses over the track rails of said track section in both directions, means responsive to the reception of code pulses in both directions on opposite sides of said insulated joints for governing the release of said switch lock, and means effective only if a train shunts the track rails adjacent said insulated joints for independently governing the release of said switch lock, whereby the switch is locked by the approach of a train in either direction until that train comes within a predetermined distance of the switch.

'7. In a coded track circuit signaling system for railroads, a stretch of track having a tract; section including an outlying track switch, code transmitting means normally acting to transmit code pulses over said track stretch in each direction toward said switch, means responsive to entrance of a train into said stretch at either end for stopping transmission of code pulses in the corresponding direction in said track stretch toward said switch, code responsive means adjacent said switch responsive to the transmission of code pulses in both directions toward said switch, a switch lock for said switch, a lock relay for governing the release of said switch lock, manually operable means for energizing said lock relay only if code pulses are being received by said code responsive means in both directions over said track stretch, and means efiective while said lock relay is energized for preventing transmission of code pulses in either direction past said switch.

8. In a coded track circuit signaling system for single track railroads, a stretch of single track divided into track sections and having signals governing train movement into and through said stretch, one of said track sections including an outlying track switch, code transmitting and receiving means associated with each end of each track section and normally acting to provide code pulses at intervals in both directions of each track section, said means acting in response to the entrance of a train into said stretch at either end to stop transmission of .code pulses in each track section toward the other end, a manually operable switch lock for said outlying switch, a lock relay acting when deenergized to prevent operswitch in either direction.

JAMES J. VAN HORN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,344,573 Van Horn Mar. 21, 1944 2,349,680 Shields May 23, 1944 2,357,240 Van Horn Aug. 29, 1944 Re. 21,783 Blosser Apr. 29, 1941 2,244,901 Staples June 10, 1941 

